Heterocyclic compound, light-emitting element, light-emitting device, electronic appliance, and lighting device

ABSTRACT

A novel heterocyclic compound is provided. A novel heterocyclic compound that can be used for a light-emitting element is provided. A novel heterocyclic compound that can improve the reliability of a light-emitting element when used for a light-emitting element is provided. A light-emitting element, a light-emitting device, an electronic appliance, or a lighting device which includes the novel heterocyclic compound and is highly reliable is provided. One embodiment of the present invention is a heterocyclic compound represented by a general formula (G0). In the general formula (G0), A represents a dibenzo[f,h]quinoxalinyl group, B represents a substituted or unsubstituted fluorenyl group, and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms. 
       A-Ar—B  (G0)

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a fabricationmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. In particular, oneembodiment of the present invention relates to a semiconductor device, adisplay device, a light-emitting device, a driving method thereof, or afabrication method thereof. In particular, one embodiment of the presentinvention relates to a heterocyclic compound and a novel method ofsynthesizing the same. In addition, one embodiment of the presentinvention relates to a light-emitting element, a light-emitting device,an electronic appliance, and a lighting device that include theheterocyclic compound.

2. Description of the Related Art

A light-emitting element using an organic compound as a luminous body,which has features such as thinness, lightness, high-speed response, andDC drive at low voltage, is expected to be used in a next-generationflat panel display. In particular, a display device in whichlight-emitting elements are arranged in matrix is considered to haveadvantages in a wide viewing angle and excellent visibility over aconventional liquid crystal display device.

The light emission mechanism is said to be as follows: when a voltage isapplied between a pair of electrodes with an EL layer including aluminous body provided therebetween, electrons injected from the cathodeand holes injected from the anode recombine in the light emission centerof the EL layer to form molecular excitons, and energy is released andlight is emitted when the molecular excitons return to the ground state.Singlet excitation and triplet excitation are known as excited states,and it is thought that light emission can be achieved through either ofthe excited states.

An organic compound is mainly used for an EL layer in such alight-emitting element and greatly affects an improvement in thecharacteristics of the light-emitting element. For this reason, avariety of novel organic compounds have been developed (e.g., PatentDocument 1).

REFERENCE Patent Document

Patent Document 1: Japanese Published Patent Application No. 2011-201869

SUMMARY OF THE INVENTION

In view of the above, one embodiment of the present invention provides anovel heterocyclic compound that can be used for an EL layer to form alight-emitting element having a long lifetime. Another embodiment of thepresent invention provides a light-emitting device, an electronicappliance, and a lighting device each of which includes a light-emittingelement having a long lifetime and is highly reliable. Anotherembodiment of the present invention provides a novel light-emittingelement, a novel light-emitting device, a novel lighting device, or thelike. Note that the descriptions of these objects do not disturb theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a compound in which adibenzo[f,h]quinoxaline ring and a fluorene skeleton are bonded to eachother through an arylene group.

One embodiment of the present invention is a heterocyclic compoundrepresented by the following general formula (G0).

A-Ar—B  (G0)

In the general formula (G0), A represents a dibenzo[f,h]quinoxalinylgroup, B represents a substituted or unsubstituted fluorenyl group, andAr represents a substituted or unsubstituted arylene group having 6 to25 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G0) is a substituted or unsubstituted 2-fluorenyl group.

Another embodiment of the present invention is a heterocyclic compoundin which B in the above general formula (G0) is represented by thefollowing general formula (α).

In the general formula (α), each of R¹¹ to R¹⁹ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

Another embodiment of the present invention is a heterocyclic compoundin which B in the above general formula (G0) is represented by thefollowing general formula (β).

In the general formula (β), each of R¹⁷ and R¹⁸ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

Another embodiment of the present invention is a heterocyclic compoundrepresented by the following general formula (G1).

In the general formula (G1), one of R¹ to R¹⁰ is represented by ageneral formula (G1-1) and each of the rest of R¹ to R¹⁰ independentlyrepresents hydrogen or an alkyl group having 1 to 6 carbon atoms. In thegeneral formula (G1-1), B represents a substituted or unsubstitutedfluorenyl group and Ar represents a substituted or unsubstituted arylenegroup having 6 to 25 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G1-1) is a substituted or unsubstituted 2-fluorenyl group.

In another embodiment of the present invention, B in the above generalformula (G1-1) is represented by the following general formula (α).

In the general formula (α), each of R¹¹ to R¹⁹ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G1-1) is represented by the following general formula (β).

In the general formula (β), each of R¹⁷ and R¹⁸ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

As the arylene group having 6 to 25 carbon atoms in the above generalformulae (G0) and (G1-1), a phenyl group, a naphthyl group, a biphenylgroup, and the like can be given. Note that anthracene is excluded.Furthermore, examples of the alkyl group having 1 to 6 carbon atoms inthe above general formulae (α), (β), and (G1) are a methyl group, anethyl group, a propyl group, an isopropyl group, a butyl group, and thelike. Examples of the aryl group having 6 to 12 carbon atoms in theabove general formulae (α) and (β) are a phenyl group, a naphthyl group,a biphenyl group, and the like.

Another embodiment of the present invention is a heterocyclic compoundrepresented by the following structural formula (100).

Another embodiment of the present invention is a light-emitting elementincluding the heterocyclic compound in any of the above structures.

Another embodiment of the present invention is a light-emitting deviceincluding the light-emitting element in any of the above structures anda transistor or a substrate.

Note that one embodiment of the present invention includes not only alight-emitting device including the light-emitting element but also anelectronic appliance and a lighting device each including thelight-emitting device.

Thus, another embodiment of the present invention is an electronicappliance including the above-described light-emitting device and amicrophone, a camera, a button for operation, an external connectionportion, or a speaker. Another embodiment of the present invention is anelectronic appliance including the above-described light-emitting deviceand a housing, a cover, or a support.

The light-emitting device in this specification refers to an imagedisplay device and a light source (e.g., a lighting device). Inaddition, the light-emitting device includes, in its category, all of amodule in which a light-emitting device is connected to a connector suchas a flexible printed circuit (FPC), a tape carrier package (TCP), amodule in which a printed wiring board is provided on the tip of a TCP,and a module in which an integrated circuit (IC) is directly mounted ona light-emitting element by a chip on glass (COG) method.

According to one embodiment of the present invention, a novelheterocyclic compound can be provided. Since the novel heterocycliccompound which is one embodiment of the present invention has astructure in which a dibenzo[f,h]quinoxaline ring is bonded to afluorene skeleton through an arylene group, the heterocyclic compoundhas higher solubility than the structure not having a fluorene skeleton.The high solubility allows the novel heterocyclic compound which is oneembodiment of the present invention to be synthesized with reducedimpurities; thus, the heterocyclic compound can be highly purified. Byusing such a high-purity heterocyclic compound as an EL material, alight-emitting element, a light-emitting device, an electronicappliance, or a lighting device which is novel and highly reliable canbe provided. A material, a compound, a light-emitting element, or thelike which is novel can also be provided. Note that the description ofthese effects does not disturb the existence of other effects. Oneembodiment of the present invention does not necessarily achieve all theobjects listed above. Other effects will be apparent from and can bederived from the description of the specification, the drawings, theclaims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a structure of a light-emitting element;

FIGS. 2A and 2B each illustrate a structure of a light-emitting element;

FIGS. 3A and 3B illustrate a light-emitting device;

FIGS. 4A to 4D′2 illustrate electronic appliances;

FIGS. 5A to 5C illustrate an electronic appliance;

FIG. 6 illustrates lighting devices;

FIGS. 7A and 7B show ¹H-NMR charts of a heterocyclic compoundrepresented by a structural formula (100);

FIG. 8 illustrates a structure of light-emitting elements in Example 2;

FIG. 9 shows voltage-luminance characteristics of light-emittingelements 1 and 2;

FIG. 10 shows luminance-current efficiency characteristics of thelight-emitting elements 1 and 2;

FIG. 11 shows reliability of the light-emitting element 1 and acomparison light-emitting element 3; and

FIG. 12 shows results of LC/MS measurements of the heterocyclic compoundrepresented by the structural formula (100).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. Note that the present inventionis not limited to the following description, and various changes andmodifications can be made without departing from the spirit and scope ofthe present invention. Therefore, the present invention should not beconstrued as being limited to the description in the followingembodiments.

Embodiment 1

In this embodiment, a heterocyclic compound which is one embodiment ofthe present invention is described. The heterocyclic compound which isone embodiment of the present invention is a dibenzo[f,h]quinoxalinederivative and has a structure in which a dibenzo[f,h]quinoxaline ringand a fluorene skeleton are bonded to each other through an arylenegroup.

One embodiment of the present invention is a heterocyclic compoundrepresented by the following general formula (G0).

A-Ar—B  (G0)

In the general formula (G0), A represents a dibenzo[f,h]quinoxalinylgroup, B represents a substituted or unsubstituted fluorenyl group, andAr represents a substituted or unsubstituted arylene group having 6 to25 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G0) is a substituted or unsubstituted 2-fluorenyl group.

Another embodiment of the present invention is a heterocyclic compoundin which B in the above general formula (G0) is represented by thefollowing general formula (α).

In the general formula (α), each of R¹¹ to R¹⁹ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

Another embodiment of the present invention is a heterocyclic compoundin which B in the above general formula (G0) is represented by thefollowing general formula (β).

In the general formula (β), each of R¹⁷ and R¹⁸ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

Another embodiment of the present invention is a heterocyclic compoundrepresented by the following general formula (G1).

In the general formula (G1), one of R¹ to R¹⁰ is represented by ageneral formula (G1-1) and each of the rest of R¹ to R¹⁰ independentlyrepresents hydrogen or an alkyl group having 1 to 6 carbon atoms. In thegeneral formula (G1-1), B represents a substituted or unsubstitutedfluorenyl group and Ar represents a substituted or unsubstituted arylenegroup having 6 to 25 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G1-1) is a substituted or unsubstituted 2-fluorenyl group.

In another embodiment of the present invention, B in the above generalformula (G1-1) is represented by the following general formula (α).

In the general formula (α), each of R¹¹ to R¹⁹ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

In another embodiment of the present invention, B in the above generalformula (G1-1) is represented by the following general formula (β).

In the general formula (β), each of R¹⁷ and R¹⁸ independently representshydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl grouphaving 6 to 12 carbon atoms.

As the arylene group having 6 to 25 carbon atoms in the above generalformulae (G0) and (G1-1), a phenyl group, a naphthyl group, a biphenylgroup, and the like can be given. Specific examples are a 1,2-, 1,3-,and 1,4-phenylene groups, a 2,6-, 3,5-, and 2,4-toluylene groups, a4,6-dimethylbenzene-1,3-diyl group, a 2,4,6-trimethylbenzene-1,3-diylgroup, a 2,3,5,6-tetramethylbenzene-1,4-diyl group, a 3,3′-, 3,4′-, and4,4′-biphenylene groups, a 1,1′:3′,1″-terbenzene-3,3″-diyl group, a1,1′:4′,1″-terbenzene-3,3″-diyl group, a 1,1′:4′,1″-terbenzene-4,4″-diylgroup, a 1,1′:3′,1″:3″,1′″-quaterbenzene-3,3′″-diyl group, a1,1′:3′,1″:4″,1″-quaterbenzene-3,4′″-diyl group, a1,1′:4′,1″:4″,1″-quaterbenzene-4,4′″-diyl group, a 1,4-, 1,5-, 2,6-, and2,7-naphthylene groups, a 2,7-fluorenylene group, a9,9-dimethyl-2,7-fluorenylene group, a 9,9-diphenyl-2,7-fluorenylenegroup, a 9,9-dimethyl-1,4-fluorenylene group, aspiro-9,9′-bifluorene-2,7-diyl group, a9,10-dihydro-2,7-phenanthrenylene group, a 2,7-phenanthrenylene group, a3,6-phenanthrenylene group, a 9,10-phenanthrenylene group, a2,7-triphenylene group, a 3,6-triphenylene group, a2,8-benzo[a]phenanthrenylene group, a 2,9-benzo[a]phenanthrenylenegroup, a 5,8-benzo[c]phenanthrenylene group, and the like. Note thatanthracene is excluded. In addition, there is no limitation on thebonding position. Furthermore, specific examples of the alkyl grouphaving 1 to 6 carbon atoms in the above general formulae (α), (β), and(G1) are a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, a sec-butyl group, an isobutyl group, a tert-butylgroup, a pentyl group, an isopentyl group, a sec-pentyl group, atert-pentyl group, a neopentyl group, a hexyl group, an isohexyl group,a sec-hexyl group, a tert-hexyl group, a neohexyl group, a3-methylpentyl group, a 2-methylpentyl group, a 2-ethylbutyl group, a1,2-dimethylbutyl group, a 2,3-dimethylbutyl group, and the like.Specific examples of the aryl group having 6 to 12 carbon atoms in theabove general formulae (α) and (β) are a phenyl group, a naphthyl group,a biphenyl group, and the like. Note that there is no limitation on thebonding position.

Next, as an example of a method of synthesizing the heterocycliccompound which is one embodiment of the present invention, an example ofa method of synthesizing the dibenzo[f,h]quinoxaline derivativerepresented by the above general formula (G0) is described.

<<Method of Synthesizing dibenzo[f,h]quinoxaline Derivative Representedby General Formula (G0)>>

The dibenzo[f,h]quinoxaline derivative represented by the generalformula (G0) can be obtained, for example, by reacting a halogencompound (A1) of a dibenzo[f,h]quinoxaline derivative with an arylboronic acid compound (A2) of a fluorene derivative, as shown in thefollowing synthesis scheme (α). Note that in the formula, X represents ahalogen element, and B¹ represents a boronic acid, a boronic ester, acyclic-triolborate salt, or the like. As the cyclic-triolborate salt, alithium salt, a potassium salt, or a sodium salt may be used.

The dibenzo[f,h]quinoxaline derivative can also be obtained in such amanner that an intermediate (B2) is obtained through a reaction with ahalogen-substituted aryl boronic acid (B1) and then made to react with aboronic acid compound (B3) of a fluorene derivative, as shown in thefollowing synthesis scheme (b).

In the above synthesis schemes (a) and (b), X represents a halogen, Arepresents a dibenzo[f,h]quinoxalinyl group, B represents a substitutedor unsubstituted fluorenyl group, and Ar represents a substituted orunsubstituted arylene group having 6 to 25 carbon atoms. Note that thehalogen X is particularly preferably chlorine, bromine, or iodine. Inthe above synthesis schemes (a) and (b), a known catalyst such as apalladium catalyst can be used. Furthermore, as the solvent, toluene,xylene, an alcohol such as ethanol, a mixed solvent thereof, or the likecan be used.

Alternatively, although not shown as a scheme, a boronic acid compoundof a dibenzo[f,h]quinoxaline derivative and a halogen compound of afluorene derivative may be reacted with each other. A reaction with ahalogen-substituted aryl boronic acid (B1) may be employed.

Since many kinds of the compounds (A1), (A2), (B1), (B2), and (B3) shownin the above synthesis schemes (a) and (b) are commercially available orcan be synthesized, many kinds of the dibenzo[f,h]quinoxaline derivativerepresented by the general formula (G0) can be synthesized. Thus, afeature of the heterocyclic compound which is one embodiment of thepresent invention is the abundance of variations.

The above is the description of the example of a method of synthesizingthe dibenzo[f,h]quinoxaline derivative which is a heterocyclic compoundas one embodiment of the present invention; however, the presentinvention is not limited thereto and another synthesis method may beemployed.

Shown below are the specific structural formulae of the heterocycliccompound (general formula (G1)) as one embodiment of the presentinvention (the following structural formulae (100) to (131)). Note thatone embodiment of the present invention is not limited thereto.

Dibenzo[f,h]quinoxaline in itself has low solubility in solvents.However, the present inventors have found that the heterocyclic compoundwhich is one embodiment of the present invention has higher solubilitythan the structure not having a fluorene skeleton because theheterocyclic compound has a structure in which a dibenzo[f,h]quinoxalineskeleton is bonded to a fluorene skeleton through an arylene group. Notethat the high solubility enables the heterocyclic compound to besynthesized with high purity. By using the obtained high-purityheterocyclic compound as an EL material, a light-emitting element, alight-emitting device, an electronic appliance, or a lighting devicewith high emission efficiency and high reliability can be achieved.Specifically, impurities can be reduced easily in the compound of oneembodiment of the present invention; therefore a light-emitting element,a light-emitting device, an electronic appliance, or a lighting devicewhich is unlikely to suffer initial deterioration can be achieved. Alight-emitting element, a light-emitting device, an electronicappliance, or a lighting device with low power consumption can also beachieved.

Furthermore, since the heterocyclic compound which is one embodiment ofthe present invention has a dibenzo[f,h]quinoxaline skeleton which is anelectron-transport skeleton and a fluorene skeleton which is ahole-transport skeleton, electrons and holes can be easily accepted.Therefore when the heterocyclic compound which is one embodiment of thepresent invention is used as a host material of a light-emitting layer,electrons and holes can recombine in a desired region in thelight-emitting layer, so that a reduction in the lifetime of alight-emitting element can be suppressed.

Furthermore, since the heterocyclic compound which is one embodiment ofthe present invention has a structure in which a dibenzo[f,h]quinoxalineskeleton is bonded to a fluorene skeleton through an arylene group,extension of a conjugated system can be inhibited and reductions in bandgap and triplet excitation energy can be prevented.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 2

In this embodiment, a light-emitting element in which the heterocycliccompound which is one embodiment of the present invention can be used asan EL material is described with reference to FIG. 1.

In a light-emitting element described in this embodiment, as illustratedin FIG. 1, an EL layer 102 including a light-emitting layer 113 isinterposed between a pair of electrodes (a first electrode (anode) 101and a second electrode (cathode) 103), and the EL layer 102 includes ahole-injection layer 111, a hole-transport layer 112, anelectron-transport layer 114, an electron-injection layer 115, and thelike in addition to the light-emitting layer 113.

When voltage is applied to such a light-emitting element, holes injectedfrom the first electrode 101 side and electrons injected from the secondelectrode 103 side recombine in the light-emitting layer 113 to raise alight-emitting substance contained in the light-emitting layer 113 to anexcited state. The light-emitting substance in the excited state emitslight when it returns to the ground state.

Although the heterocyclic compound which is one embodiment of thepresent invention can be used for any one or more layers in the EL layer102 described in this embodiment, the heterocyclic compound ispreferably used for the light-emitting layer 113, the hole-transportlayer 112, or the electron-transport layer 114. In other words, theheterocyclic compound is used in part of a light-emitting element havinga structure described below.

A preferred specific example in which the light-emitting elementdescribed in this embodiment is fabricated is described below.

As the first electrode (anode) 101 and the second electrode (cathode)103, a metal, an alloy, an electrically conductive compound, a mixturethereof, and the like can be used. Specific examples are indiumoxide-tin oxide (indium tin oxide (ITO)), indium oxide-tin oxidecontaining silicon or silicon oxide, indium oxide-zinc oxide (indiumzinc oxide), indium oxide containing tungsten oxide and zinc oxide, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),and titanium (Ti). In addition, an element belonging to Group 1 or Group2 of the periodic table, for example, an alkali metal such as lithium(Li) or cesium (Cs), an alkaline earth metal such as calcium (Ca) orstrontium (Sr), magnesium (Mg), an alloy containing such an element(MgAg or AlLi), a rare earth metal such as europium (Eu) or ytterbium(Yb), an alloy containing such an element, graphene, and the like can beused. The first electrode (anode) 101 and the second electrode (cathode)103 can be formed by, for example, a sputtering method or an evaporationmethod (including a vacuum evaporation method).

The hole-injection layer 111 injects holes into the light-emitting layer113 through the hole-transport layer 112 having a high hole-transportproperty. The hole-injection layer 111 contains a substance having ahigh hole-transport property and an acceptor substance, so thatelectrons are extracted from the substance having a high hole-transportproperty by the acceptor substance to generate holes and the holes areinjected into the light-emitting layer 113 through the hole-transportlayer 112. The hole-transport layer 112 is formed using a substancehaving a high hole-transport property.

Specific examples of the substance having a high hole-transportproperty, which is used for the hole-injection layer 111 and thehole-transport layer 112, include aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB ora-NPD),N,N-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2); and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1). Other examples include carbazole derivativessuch as 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA).The substances listed here are mainly ones that have a hole mobility of10⁻⁶ cm²/Vs or higher. Note that any substance other than the substanceslisted here may be used as long as the hole-transport property is higherthan the electron-transport property.

A high molecular compound such as poly(N-vinylcarbazole) (abbreviation:PVK), poly(-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation:PTPDMA), or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](abbreviation: Poly-TPD) can also be used.

Examples of the acceptor substance that is used for the hole-injectionlayer 111 include oxides of metals belonging to Groups 4 to 8 of theperiodic table. Specifically, molybdenum oxide is particularlypreferable.

The light-emitting layer 113 is a layer containing a light-emittingsubstance. The light-emitting layer 113 may contain only alight-emitting substance; alternatively, an emission center substance(guest material) may be dispersed in a host material in thelight-emitting layer 113. Note that as the host material, theabove-described substance having a high hole-transport property or alater-described substance having a high electron-transport property canbe used, and preferably, a substance having high triplet excitationenergy is used. In addition, the heterocyclic compound described inEmbodiment 1 which is one embodiment of the present invention can beused in combination.

There is no particular limitation on the material that can be used asthe light-emitting substance and the emission center substance in thelight-emitting layer 113. A light-emitting substance converting singletexcitation energy into luminescence (hereinafter, referred to asfluorescent substance) or a light-emitting substance converting tripletexcitation energy into luminescence (hereinafter, referred to asphosphorescent substance) can be used. Examples of the light-emittingsubstance and the emission center substance are given below.

As an example of the light-emitting substance converting singletexcitation energy into luminescence, a substance emitting fluorescencecan be given.

Examples of the substance emitting fluorescence includeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N″,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM).

Examples of the light-emitting substance converting triplet excitationenergy into luminescence include a substance emitting phosphorescenceand a thermally activated delayed fluorescence (TADF) material. Notethat “delayed fluorescence” exhibited by the TADF material refers tolight emission having the same spectrum as normal fluorescence and anextremely long lifetime. The lifetime is 10⁻⁶ seconds or longer,preferably 10⁻³ seconds or longer.

Examples of the substance emitting phosphorescence include bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), tris(acetylacetonato) (monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)), bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]),(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)₂(dpm)],(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)₃(Phen)), andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)₃(Phen)).

Preferable examples of the substance (i.e., host material) used fordispersing the light-emitting substance converting triplet excitationenergy into luminescence include compounds having an arylamine skeleton,such as 2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn)and NPB, carbazole derivatives such as CBP and4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), andmetal complexes such as bis[2-(2-hydroxyphenyl)pyridinato]zinc(abbreviation: Znpp₂), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), and tris(8-quinolinolato)aluminum (abbreviation: Alq₃).Alternatively, a high molecular compound such as PVK can be used.

Examples of the TADF material includes fullerene, a derivative thereof,an acridine derivative such as proflavine, and eosin. Other examplesinclude a metal-containing porphyrin, such as a porphyrin containingmagnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium(In), or palladium (Pd). Examples of the metal-containing porphyrininclude a protoporphyrin-tin fluoride complex (SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂OEP). Alternatively,a heterocyclic compound including a π-electron rich heteroaromatic ringand a π-electron deficient heteroaromatic ring can be used, such as2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(PIC-TRZ). Note that a material in which the π-electron richheteroaromatic ring is directly bonded to the π-electron deficientheteroaromatic ring is particularly preferably used because both thedonor property of the π-electron rich heteroaromatic ring and theacceptor property of the π-electron deficient heteroaromatic ring areincreased and the energy difference between the S₁ level and the T₁level becomes small.

When the light-emitting layer 113 includes one or more kinds of hostmaterials and a light-emitting substance converting singlet excitationenergy into luminescence or any of the light-emitting substancesconverting triplet excitation energy into luminescence (i.e., a guestmaterial), light emission with high emission efficiency can be obtainedfrom the light-emitting layer 113. When two or more kinds of hostmaterials are used, they are preferably a combination which can form anexciplex.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property. For the electron-transportlayer 114, a metal complex such as tris(8-quinolinolato)aluminum(abbreviation: Alq₃), tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂), or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂) can be used. Alternatively, a heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4′-tert-butylphenyl)-4-phenyl-5-(4″-biphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can alsobe used. A high molecular compound such aspoly(2,5-pyridinediyl)(abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py) orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can also be used. The substances listed here aremainly ones that have an electron mobility of 1×10⁻⁶ cm²/Vs or higher.Note that any substance other than the substances listed here may beused for the electron-transport layer 114 as long as theelectron-transport property is higher than the hole-transport property.The heterocyclic compound described in Embodiment 1 which is oneembodiment of the present invention can also be used.

The electron-transport layer 114 is not limited to a single layer, butmay be a stack of two or more layers each containing any of thesubstances listed above.

The electron-injection layer 115 is a layer containing a substancehaving a high electron-injection property. For the electron-injectionlayer 115, an alkali metal, an alkaline earth metal, or a compoundthereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF₂), or lithium oxide (LiO_(x)) can be used. A rare earthmetal compound like erbium fluoride (ErF₃) can also be used. Anelectride may also be used for the electron-injection layer 115.Examples of the electride include a substance in which electrons areadded at high concentration to calcium oxide-aluminum oxide. Any of thesubstances for forming the electron-transport layer 114, which are givenabove, can be used.

A composite material in which an organic compound and an electron donor(donor) are mixed may also be used for the electron-injection layer 115.Such a composite material is excellent in an electron-injection propertyand an electron-transport property because electrons are generated inthe organic compound by the electron donor. In this case, the organiccompound is preferably a material that is excellent in transporting thegenerated electrons. Specifically, for example, the substances forforming the electron-transport layer 114 (e.g., a metal complex or aheteroaromatic compound), which are given above, can be used. As theelectron donor, a substance showing an electron-donating property withrespect to the organic compound may be used. Specifically, an alkalimetal, an alkaline earth metal, and a rare earth metal are preferable,and lithium, cesium, magnesium, calcium, erbium, and ytterbium aregiven. In addition, an alkali metal oxide or an alkaline earth metaloxide is preferable, and lithium oxide, calcium oxide, and barium oxideare given. A Lewis base such as magnesium oxide can also be used. Anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can alsobe used.

Note that each of the above-described hole-injection layer 111,hole-transport layer 112, light-emitting layer 113, electron-transportlayer 114, and electron-injection layer 115 can be formed by a methodsuch as an evaporation method (e.g., a vacuum evaporation method), anink-jet method, or a coating method.

In the above-described light-emitting element, current flows because ofa potential difference generated between the first electrode 101 and thesecond electrode 103 and holes and electrons are recombined in the ELlayer 102, whereby light is emitted. Then, the emitted light isextracted outside through one or both of the first electrode 101 and thesecond electrode 103. Thus, one or both of the first electrode 101 andthe second electrode 103 are electrodes having light-transmittingproperties.

The light-emitting element described in this embodiment is an example ofa light-emitting element in which the heterocyclic compound which is oneembodiment of the present invention is used as an EL material. Note thatthe heterocyclic compound which is one embodiment of the presentinvention has high solubility and is easy to purify by sublimation insynthesis; therefore it can be highly purified. Accordingly, by usingthe heterocyclic compound which is one embodiment of the presentinvention, a highly reliable light-emitting element can be obtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 3

Described in this embodiment is a light-emitting element (hereinafter, atandem light-emitting element) which has a structure in which acharge-generation layer is provided between a plurality of EL layers andthe heterocyclic compound which is one embodiment of the presentinvention is used as an EL material in the EL layers.

A light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 202(1) and a second EL layer 202(2)) between a pair of electrodes(a first electrode 201 and a second electrode 204), as illustrated inFIG. 2A.

In this embodiment, the first electrode 201 functions as an anode, andthe second electrode 204 functions as a cathode. Note that the firstelectrode 201 and the second electrode 204 can have structures similarto those described in Embodiment 2. In addition, either or both of theEL layers (the first EL layer 202(1) and the second EL layer 202(2)) mayhave structures similar to those described in Embodiment 2. In otherwords, the structures of the first EL layer 202(1) and the second ELlayer 202(2) may be the same or different from each other and can besimilar to those of the EL layers described in Embodiment 2.

In addition, a charge-generation layer 205 is provided between theplurality of EL layers (the first EL layer 202(1) and the second ELlayer 202(2)). The charge-generation layer 205 has a function ofinjecting electrons into one of the EL layers and injecting holes intothe other of the EL layers when voltage is applied between the firstelectrode 201 and the second electrode 204. In this embodiment, whenvoltage is applied such that the potential of the first electrode 201 ishigher than that of the second electrode 204, the charge-generationlayer 205 injects electrons into the first EL layer 202(1) and injectsholes into the second EL layer 202(2).

Note that in terms of light extraction efficiency, the charge-generationlayer 205 preferably has a property of transmitting visible light(specifically, the charge-generation layer (I) 205 has a visible lighttransmittance of 40% or more). The charge-generation layer 205 functionseven when it has lower conductivity than the first electrode 201 or thesecond electrode 204.

The charge-generation layer 205 may have either a structure in which anelectron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, as theorganic compound having a high hole-transport property, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or BSPB, or thelike can be used. The substances listed here are mainly ones that have ahole mobility of 10⁻⁶ cm²/Vs or higher. Note that any organic compoundother than the compounds listed here may be used as long as thehole-transport property is higher than the electron-transport property.

As the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. Oxides of metalsbelonging to Groups 4 to 8 of the periodic table can also be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because of their high electron-acceptingproperties. Among these, molybdenum oxide is especially preferablebecause it is stable in the air, has a low hygroscopic property, and iseasy to handle.

In the case of the structure in which an electron donor is added to anorganic compound having a high electron-transport property, as theorganic compound having a high electron-transport property, for example,a metal complex having a quinoline skeleton or a benzoquinolineskeleton, such as Alq, Almq₃, BeBq₂, or BAlq, or the like can be used.Alternatively, a metal complex having an oxazole-based ligand or athiazole-based ligand, such as Zn(BOX)₂ or Zn(BTZ)₂ can be used.Alternatively, in addition to such a metal complex, PBD, OXD-7, TAZ,Bphen, BCP, or the like can be used. The substances listed here aremainly ones that have an electron mobility of 10⁻⁶ cm²/Vs or higher.Note that any organic compound other than the compounds listed here maybe used as long as the electron-transport property is higher than thehole-transport property.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, metals belonging to Groups 2and 13 of the periodic table, or an oxide or carbonate thereof.Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or thelike is preferably used. Alternatively, an organic compound such astetrathianaphthacene may be used as the electron donor.

Note that forming the charge-generation layer 205 by using any of theabove materials can suppress a drive voltage increase caused by thestack of the EL layers.

Although the light-emitting element including two EL layers is describedin this embodiment, the present invention can be similarly applied to alight-emitting element in which n EL layers (202(1) to 202(n)) (n isthree or more) are stacked as illustrated in FIG. 2B. In the case wherea plurality of EL layers are included between a pair of electrodes as inthe light-emitting element according to this embodiment, by providingcharge-generation layers (205(1) to 205(n−1)) between the EL layers,light emission in a high luminance region can be obtained with currentdensity kept low. Since the current density can be kept low, the elementcan have a long lifetime. When the light-emitting element is applied tolight-emitting devices, electronic appliances, and lighting devices eachhaving a large light-emitting area, voltage drop due to resistance of anelectrode material can be reduced, which results in uniform lightemission in a large area.

When the EL layers have different emission colors, a desired emissioncolor can be obtained from the whole light-emitting element. Forexample, in the light-emitting element having two EL layers, when anemission color of the first EL layer and an emission color of the secondEL layer are made to be complementary colors, a light-emitting elementemitting white light as a whole light-emitting element can also beobtained. Note that “complementary colors” refer to colors that canproduce an achromatic color when mixed. In other words, emission ofwhite light can be obtained by mixture of light emitted from substanceswhose emission colors are complementary colors.

The same can be applied to a light-emitting element having three ELlayers. For example, the light-emitting element as a whole can providewhite light emission when the emission color of the first EL layer isred, the emission color of the second EL layer is green, and theemission color of the third EL layer is blue.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 4

Described in this embodiment is a light-emitting device that includes alight-emitting element in which the heterocyclic compound which is oneembodiment of the present invention is used for an EL layer.

The light-emitting device may be either a passive matrix typelight-emitting device or an active matrix type light-emitting device.Note that any of the light-emitting elements described in the otherembodiments can be used for the light-emitting device described in thisembodiment.

In this embodiment, an active matrix light-emitting device is describedwith reference to FIGS. 3A and 3B.

Note that FIG. 3A is a top view illustrating a light-emitting device andFIG. 3B is a cross-sectional view taken along the chain line A-A′ inFIG. 3A. The active matrix light-emitting device according to thisembodiment includes a pixel portion 302 provided over an elementsubstrate 301, a driver circuit portion (a source line driver circuit)303, and driver circuit portions 304 a and 304 b. The pixel portion 302,the driver circuit portion 303, and the driver circuit portions 304 aand 304 b are sealed between the element substrate 301 and a sealingsubstrate 306 with a sealant 305.

In addition, over the element substrate 301, a lead wiring 307 forconnecting an external input terminal, through which a signal (e.g., avideo signal, a clock signal, a start signal, a reset signal, or thelike) or electric potential from the outside is transmitted to thedriver circuit portion 303 and the driver circuit portions 304 a and 304b, is provided. Here, an example is described in which a flexibleprinted circuit (FPC) 308 is provided as the external input terminal.Although only the FPC is illustrated here, the FPC may be provided witha printed wiring board (PWB). The light-emitting device in thisspecification includes, in its category, not only the light-emittingdevice itself but also the light-emitting device provided with the FPCor the PWB.

Next, a cross-sectional structure is described with reference to FIG.3B. The driver circuit portion and the pixel portion are formed over theelement substrate 301; the driver circuit portion 303 that is the sourceline driver circuit and the pixel portion 302 are illustrated here.

The driver circuit portion 303 is an example in which an FET 309 and anFET 310 are combined. Note that the driver circuit portion 303 may beformed with a circuit including transistors having the same conductivitytype (either n-channel transistors or p-channel transistors) or a CMOScircuit including an n-channel transistor and a p-channel transistor.Although this embodiment shows a driver integrated type in which thedriver circuit is formed over the substrate, the driver circuit is notnecessarily formed over the substrate, and may be formed outside thesubstrate.

The pixel portion 302 includes a plurality of pixels each of whichincludes a switching FET 311, a current control FET 312, and a firstelectrode (anode) 313 which is electrically connected to a wiring (asource electrode or a drain electrode) of the current control FET 312.Although the pixel portion 302 includes two FETs, the switching FET 311and the current control FET 312, in this embodiment, one embodiment ofthe present invention is not limited thereto. The pixel portion 302 mayinclude, for example, three or more FETs and a capacitor in combination.

As the FETs 309, 310, 311, and 312, for example, a staggered transistoror an inverted staggered transistor can be used. For example, a Group 13semiconductor (e.g., gallium), a Group 14 semiconductor (e.g., silicon),a compound semiconductor, an oxide semiconductor, or an organicsemiconductor can be used. In addition, there is no particularlimitation on the crystallinity of the semiconductor material, and anamorphous semiconductor or a crystalline semiconductor can be used. Inparticular, an oxide semiconductor is preferably used for the FETs 309,310, 311, and 312. Examples of the oxide semiconductor include an In—Gaoxide and an In-M-Zn oxide (M is Al, Ga, Y, Zr, La, Ce, or Nd). Forexample, an oxide semiconductor that has an energy gap of 2 eV or more,preferably 2.5 eV or more, further preferably 3 eV or more is used forthe FETs 309, 310, 311, and 312, so that the off-state current of thetransistors can be reduced.

In addition, an insulator 314 is formed to cover end portions of thefirst electrode (anode) 313. In this embodiment, the insulator 314 isformed using a positive photosensitive acrylic resin. The firstelectrode 313 is used as an anode in this embodiment.

The insulator 314 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof. This enables thecoverage with a film to be formed over the insulator 314 to befavorable. The insulator 314 can be formed using, for example, either anegative photosensitive resin or a positive photosensitive resin. Thematerial of the insulator 314 is not limited to an organic compound andan inorganic compound such as silicon oxide, silicon oxynitride, orsilicon nitride can also be used.

An EL layer 315 and a second electrode (cathode) 316 are stacked overthe first electrode (anode) 313. In the EL layer 315, at least alight-emitting layer is provided. In the EL layer 315, a hole-injectionlayer, a hole-transport layer, an electron-transport layer, anelectron-injection layer, a charge-generation layer, and the like can beprovided as appropriate in addition to the light-emitting layer.

A light-emitting element 317 is formed of a stack of the first electrode(anode) 313, the EL layer 315, and the second electrode (cathode) 316.For the first electrode (anode) 313, the EL layer 315, and the secondelectrode (cathode) 316, any of the materials given in Embodiment 2 canbe used. Although not illustrated, the second electrode (cathode) 316 iselectrically connected to the FPC 308 which is an external inputterminal.

Although the cross-sectional view in FIG. 3B illustrates only onelight-emitting element 317, a plurality of light-emitting elements arearranged in a matrix in the pixel portion 302. Light-emitting elementsthat emit light of three kinds of colors (R, G, and B) are selectivelyformed in the pixel portion 302, whereby a light-emitting device capableof full color display can be obtained. In addition to the light-emittingelements that emit light of three kinds of colors (R, G, and B), forexample, light-emitting elements that emit light of white (W), yellow(Y), magenta (M), cyan (C), and the like may be formed. For example, thelight-emitting elements that emit light of a plurality of kinds ofcolors are used in combination with the light-emitting elements thatemit light of three kinds of colors (R, G, and B), whereby effects suchas an improvement in color purity and a reduction in power consumptioncan be obtained. Alternatively, the light-emitting device may be capableof full color display by combination with color filters. Thelight-emitting device may have improved emission efficiency and reducedpower consumption by combination with quantum dots.

Furthermore, the sealing substrate 306 is attached to the elementsubstrate 301 with the sealant 305, whereby a light-emitting element 317is provided in a space 318 surrounded by the element substrate 301, thesealing substrate 306, and the sealant 305. Note that the space 318 maybe filled with an inert gas (such as nitrogen and argon) or the sealant305.

An epoxy-based resin or glass frit is preferably used for the sealant305. The material preferably allows as little moisture and oxygen aspossible to penetrate. As the sealing substrate 306, a glass substrate,a quartz substrate, or a plastic substrate formed of fiber-reinforcedplastic (FRP), polyvinyl fluoride) (PVF), polyester, acrylic, or thelike can be used. In the case where glass frit is used as the sealant,the element substrate 301 and the sealing substrate 306 are preferablyglass substrates for high adhesion

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, examples of an electronic appliance manufacturedusing a light-emitting device which is one embodiment of the presentinvention are described with reference to FIGS. 4A to 4D.

Examples of the electronic appliance including the light-emitting deviceare television devices (also referred to as TV or television receivers),monitors for computers and the like, cameras such as digital cameras anddigital video cameras, digital photo frames, cellular phones (alsoreferred to as portable telephone devices), portable game consoles,portable information terminals, audio playback devices, large gamemachines such as pachinko machines, and the like. Specific examples ofthe electronic appliances are illustrated in FIGS. 4A to 4D.

FIG. 4A illustrates an example of a television device. In the televisiondevice 7100, a display portion 7103 is incorporated in a housing 7101.The display portion 7103 can display images and may be a touch panel (aninput/output device) including a touch sensor (an input device). Notethat the light-emitting device which is one embodiment of the presentinvention can be used for the display portion 7103. In addition, here,the housing 7101 is supported by a stand 7105.

The television device 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasts can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 4B illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer can be manufactured using the light-emitting device whichis one embodiment of the present invention for the display portion 7203.The display portion 7203 may be a touch panel (an input/output device)including a touch sensor (an input device).

FIG. 4C illustrates a smart watch, which includes a housing 7302, adisplay panel 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like.

The display panel 7304 mounted in the housing 7302 serving as a bezelincludes a non-rectangular display region. The display panel 7304 candisplay an icon 7305 indicating time, another icon 7306, and the like.The display panel 7304 may be a touch panel (an input/output device)including a touch sensor (an input device).

The smart watch illustrated in FIG. 4C can have a variety of functions,for example, a function of displaying a variety of information (e.g., astill image, a moving image, and a text image) on a display portion, atouch panel function, a function of displaying a calendar, date, time,and the like, a function of controlling processing with a variety ofsoftware (programs), a wireless communication function, a function ofbeing connected to a variety of computer networks with a wirelesscommunication function, a function of transmitting and receiving avariety of data with a wireless communication function, and a functionof reading program or data stored in a recording medium and displayingthe program or data on a display portion.

The housing 7302 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. Note that the smart watch can be manufacturedusing the light-emitting device for the display panel 7304.

FIG. 4D illustrates an example of a cellular phone (e.g., smartphone). Acellular phone 7400 includes a housing 7401 provided with a displayportion 7402, a microphone 7406, a speaker 7405, a camera 7407, anexternal connection portion 7404, an operation button 7403, and thelike. In the case where a light-emitting device is manufactured byforming a light-emitting element of one embodiment of the presentinvention over a flexible substrate, the light-emitting element can beused for the display portion 7402 having a curved surface as illustratedin FIG. 4D.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 4D is touched with a finger or the like, data can be input to thecellular phone 7400. In addition, operations such as making a call andcomposing an e-mail can be performed by touch on the display portion7402 with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting data such as characters. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are combined.

For example, in the case of making a call or creating e-mail, acharacter input mode mainly for inputting characters is selected for thedisplay portion 7402 so that characters displayed on the screen can beinput. In this case, it is preferable to display a keyboard or numberbuttons on almost the entire screen of the display portion 7402.

When a detection device such as a gyroscope or an acceleration sensor isprovided inside the cellular phone 7400, display on the screen of thedisplay portion 7402 can be automatically changed by determining theorientation of the cellular phone 7400 (whether the cellular phone isplaced horizontally or vertically for a landscape mode or a portraitmode).

The screen modes are changed by touch on the display portion 7402 oroperation with the button 7403 of the housing 7401. The screen modes canbe switched depending on the kind of images displayed on the displayportion 7402. For example, when a signal of an image displayed on thedisplay portion is a signal of moving image data, the screen mode isswitched to the display mode. When the signal is a signal of text data,the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. In addition, by providing abacklight or a sensing light source that emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

The light-emitting device can be used for a cellular phone having astructure illustrated in FIG. 4D′1 or FIG. 4D′2, which is anotherstructure of the cellular phone (e.g., smartphone).

Note that in the case of the structure illustrated in FIG. 4D′1 or FIG.4D′2, text data, image data, or the like can be displayed on secondscreens 7502(1) and 7502(2) of housings 7500(1) and 7500(2) as well asfirst screens 7501(1) and 7501(2). Such a structure enables a user toeasily see text data, image data, or the like displayed on the secondscreens 7502(1) and 7502(2) while the cellular phone is placed in user'sbreast pocket.

FIGS. 5A to 5C illustrate a foldable portable information terminal 9310.FIG. 5A illustrates the portable information terminal 9310 which isopened. FIG. 5B illustrates the portable information terminal 9310 whichis being opened or being folded. FIG. 5C illustrates the portableinformation terminal 9310 that is folded. The portable informationterminal 9310 is highly portable when folded. When the portableinformation terminal 9310 is opened, a seamless large display region ishighly browsable.

A display panel 9311 is supported by three housings 9315 joined togetherby hinges 9313. Note that the display panel 9311 may be a touch panel(an input/output device) including a touch sensor (an input device). Bybending the display panel 9311 at a connection portion between twohousings 9315 with the use of the hinges 9313, the portable informationterminal 9310 can be reversibly changed in shape from an opened state toa folded state. A light-emitting device of one embodiment of the presentinvention can be used for the display panel 9311. A display region 9312is a display region that positioned at a side surface of the portableinformation terminal 9310 that is folded. On the display region 9312,information icons, file shortcuts of frequently used applications orprograms, and the like can be displayed, and confirmation of informationand start of application can be smoothly performed.

As described above, the electronic appliances can be obtained using thelight-emitting device which is one embodiment of the present invention.Note that the light-emitting device can be used for electronicappliances in a variety of fields without being limited to theelectronic appliances described in this embodiment.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 6

In this embodiment, examples of a lighting device including thelight-emitting device which is one embodiment of the present inventionare described with reference to FIG. 6.

FIG. 6 illustrates an example in which the light-emitting device is usedas an indoor lighting device 8001. Since the light-emitting device canhave a large area, it can be used for a lighting device having a largearea. In addition, with the use of a housing with a curved surface, alighting device 8002 which includes the housing, a cover, and a supportand in which a light-emitting region has a curved surface can also beobtained. A light-emitting element included in the light-emitting devicedescribed in this embodiment is in a thin film form, which allows thehousing to be designed more freely. Thus, the lighting device can beelaborately designed in a variety of ways. In addition, a wall of theroom may be provided with a large-sized lighting device 8003.

When the light-emitting device is used for a table by being used as asurface of a table, a lighting device 8004 that has a function as atable can be obtained. When the light-emitting device is used as part ofother furniture, a lighting device that functions as the furniture canbe obtained.

As described above, a variety of lighting devices that include thelight-emitting device can be obtained. Note that these lighting devicesare also embodiments of the present invention.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1 Synthesis Example

In this example, a method of synthesizing the heterocyclic compoundwhich is one embodiment of the present invention,2-{3-[3-(9,9-dimethylfluoren-2-yl)phenyl]phenyl}dibenzo[f,h]quinoxaline(abbreviation: 2mFBPDBq) (structural formula (100)), is described. Notethat a structure of 2mFBPDBq is shown below.

Step 1: Synthesis of2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dimethylfluorene

First, into a 100-mL three-neck flask were put 5.0 g (18 mmol) of2-bromo-9,9-dimethylfluorene, 5.1 g (20 mmol) of4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi-1,3,2-dioxaborolane, 5.4 g (55mmol) of potassium acetate, and 61 mL of 1,4-dioxane. This mixture wasdegassed by being stirred under reduced pressure, and the air in theflask was replaced with nitrogen.

Then, to the mixture, 0.75 mg (0.92 mmol) of[1,1′-bis(diphenylphosphino)fenocene]palladium(II) dichloride was added.This mixture was stirred at 90° C. under a nitrogen stream for 8 hours.After the predetermined time elapsed, this mixture was suction-filteredthrough Celite, and the obtained filtrate was concentrated to give anoily substance. This solid was recrystallized from ethanol to give 4.4 gof a brown solid in 75% yield.

The synthesis scheme of the step 1 is shown in (A−1).

Step 2: Synthesis of 2-(3-bromophenyl)-9,9-dimethylfluorene

Next, into a 200-mL three-neck flask were put 5.9 g (18 mmol) of2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dimethylfluorene,which was obtained in the above step 1, and 5.7 g (20 mmol) of3-bromoiodobenzene. To this were added 18 mL of a 2M aqueous solution ofpotassium carbonate, 92 mL of toluene, and 23 mL of ethanol.

The mixture was degassed by being stirred under reduced pressure, andthe air in the flask was replaced with nitrogen. To this mixture wasadded 0.082 mg (0.37 mmol) of palladium(II) acetate. This mixture wasstirred at 80° C. under a nitrogen stream for 8 hours.

After the predetermined time elapsed, water and toluene were added tothis mixture, and the aqueous layer of the obtained filtrate wassubjected to extraction with toluene. The obtained extract solution andthe organic layer were combined, washed with an aqueous solution ofsodium hydrogen carbonate and saturated brine, and dried with magnesiumsulfate. The obtained mixture was gravity-filtered, and the filtrate wasconcentrated to give an oily substance. Hexane and acetonitrile wereadded to this oily substance, and the acetonitrile layer of the obtainedfiltrate was subjected to extraction with hexane. The obtained extractsolution and the hexane layer were combined and concentrated to give anoily substance. The obtained oily substance was recrystallized fromethanol to give 3.0 g of a white solid in 47% yield.

The synthesis scheme of the step 2 is shown in (A-2) below.

Step 3: Synthesis of2-[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-9,9-dimethylfluorene

Next, into a 3-L three-neck flask were put 130 g (0.37 mol) of2-(3-bromophenyl)-9,9-dimethylfluorene, which was obtained in the abovestep 2, and 103 g (0.41 mol) of4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi-1,3,2-dioxaborolane. To this wereadded 109 g (1.1 mol) of potassium acetate and 1.2 L ofN,N-dimethylformamide.

This mixture was degassed by being stirred under reduced pressure, andthe air in the flask was replaced with nitrogen. To the mixture wereadded 2.5 g (0.011 mol) of palladium(II) acetate, and the mixture wasstirred at 100° C. under a nitrogen stream for 5 hours. After thepredetermined time elapsed, this mixture was suction-filtered throughCelite and alumina, and the obtained filtrate was concentrated to givean oily substance. This solid was recrystallized from ethanol to give118 g of a brown solid in 81% yield.

The synthesis scheme of the step 3 is shown in (A-3) below.

Step 4: Synthesis of 2mFBPDBq

Next, into a 100-mL three-neck flask were put 3.8 g (9.7 mmol) of2-[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-9,9-dimethylfluorene),which was obtained in the above step 3, and 3.0 g (8.8 mmol) of2-(3-chlorophenyl)dibenzo[f,h]quinoxaline. To this were added 2.0 g (26mmol) of t-butanol, 5.6 g (26 mmol) of tripotassium phosphate, and 59 mLof 1,4-dioxane. This mixture was degassed by being stirred under reducedpressure, and the air in the flask was replaced with nitrogen. To thismixture were added 59 mg (0.30 mmol) of palladium(II) acetate and 0.20 g(0.60 mmol) of di(1-adamantyl)-n-butylphosphine. After a predeterminedtime elapsed, this mixture was suction-filtered through Celite, and theobtained filtrate was concentrated to give a solid. This solid waspurified by silica gel column chromatography. As a developing solvent, amixed solvent of toluene, hexane, and ethyl acetate in a ratio of10:10:1 was used. The obtained fraction was recrystallized fromacetonitrile to give 3.7 g of a white solid in 74% yield.

The synthesis scheme of the step 4 is shown in (A-4).

Analysis results by nuclear magnetic resonance (¹H-NMR) spectroscopy ofthe white solid obtained in the above step 4 are described below. FIGS.7A and 7B are ¹H-NMR charts. FIG. 7B is a chart where the range from 7(ppm) to 10 (ppm) on the horizontal axis (δ) in FIG. 7A is enlarged. Theresults show that the heterocyclic compound which is one embodiment ofthe present invention, 2mFBPDBq (structural formula (100)), was obtainedin the above step 4.

¹H NMR (CDCl₃, 500 MHz): δ (ppm)=1.55 (s, 6H), 7.32-7.38 (m, 2H), 7.47(dd, J=6.3 Hz, 1.7 Hz, 1H), 7.63 (t, J=7.5 Hz, 1H), 7.68-7.85 (m, 12H),8.00 (t, J=1.7 Hz, 1H), 8.34-8.36 (m, 1H), 8.63-8.67 (m, 3H), 9.25 (dd,J=8.0 Hz, 1.7 Hz, 1H), 9.44 (dd, J=8.0 Hz, 1.8 Hz, 1H), 9.47 (s, 1H).

By a train sublimation method, 3.0 g of the obtained white powder of2mFBPDBq was purified. In the purification by sublimation, 2mFBPDBq washeated at 300° C. under the conditions where the pressure was 2.5 Pa andthe argon flow rate was 10 mL/min. After the purification bysublimation, 1.9 g of a white powder of 2mFBPDBq was obtained at acollection rate of 63%.

Next, 2mFBPDBq was analyzed by liquid chromatography mass spectrometry(LC/MS).

The analysis by LC/MS was carried out with Acquity UPLC (manufactured byWaters Corporation), and Xevo G2 Tof MS (manufactured by WatersCorporation).

In the MS, ionization was carried out by an electrospray ionization(abbreviation: ESI) method. At this time, the capillary voltage and thesample cone voltage were set to 3.0 kV and 30 V, respectively, anddetection was performed in a positive mode. A component that underwentthe ionization under the above-described conditions was collided with anargon gas in a collision cell to dissociate into product ions. Theenergy (collision energy) for the collision with argon was 70 eV. Themass range for the measurement was m/z=100 to 1200.

FIG. 12 shows the measurement results. The results in FIG. 12 revealthat the product ions of 2mFBPDBq, which is the heterocyclic compound ofone embodiment of the present invention represented by the structuralformula (100), are detected mainly around m/z=575, around m/z=341, andaround m/z=229. Note that the results in FIG. 12 show characteristicsderived from 2mFBPDBq and thus can be regarded as important data foridentifying 2mFBPDBq contained in a mixture.

Note that the product ion around m/z=229 can be presumed to be a production of a dibenzo[f,h]quinoxaline ring; thus, it is suggested that2mFBPDBq, which is the heterocyclic organic compound of one embodimentof the present invention, includes a dibenzo[f,h]quinoxaline ring.

Example 2

In this example, a light-emitting element 1 and a light-emitting element2 each including the heterocyclic compound which is one embodiment ofthe present invention are described with reference to FIG. 8. Chemicalformulae of materials used in this example are shown below.

<<Fabrication of Light-Emitting Elements 1 and 2>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 800 by a sputtering method, whereby a firstelectrode 801 functioning as an anode was formed. Note that thethickness was set to 110 nm and the electrode area was set to 2 mm×2 mm.

Next, as pretreatment for fabricating the light-emitting elements 1 and2 over the substrate 800, UV ozone treatment was performed for 370seconds after washing of a surface of the substrate with water andbaking that was performed at 200° C. for 1 hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. in a heating chamber of thevacuum evaporation apparatus for 30 minutes, and then the substrate 800was cooled down for approximately 30 minutes.

Next, the substrate 800 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate over which thefirst electrode 801 was formed faced downward. In this example, a caseis described in which a hole-injection layer 811, a hole-transport layer812, a light-emitting layer 813, an electron-transport layer 814, and anelectron-injection layer 815, which are included in an EL layer 802, aresequentially formed by a vacuum evaporation method.

After reducing the pressure in the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were deposited by co-evaporation so that the massratio of DBT3P-II to molybdenum oxide was 4:2, whereby thehole-injection layer 811 was formed over the first electrode 801. Thethickness was 20 nm. Note that co-evaporation is an evaporation methodin which a plurality of different substances are concurrently vaporizedfrom different evaporation sources.

Next, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, wherebythe hole-transport layer 812 was formed.

Next, the light-emitting layer 813 was formed over the hole-transportlayer 812.

In the light-emitting element 1, the light-emitting layer 813 having astacked-layer structure was formed to a thickness of 40 nm as follows:2mFBPDBq,N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) were deposited by co-evaporation toa thickness of 20 nm by co-evaporation so that the mass ratio of2mFBPDBq to PCBBiF and [Ir(tBuppm)₂(acac)] was 0.7:0.3:0.05, and then2mFBPDBq, PCBBiF, and [Ir(tBuppm)₂(acac)] were deposited byco-evaporation to a thickness of 20 nm so that the mass ratio of2mFBPDBq to PCBBiF and [Ir(tBuppm)₂(acac)] was 0.8:0.2:0.05.

In the light-emitting element 2, the light-emitting layer 813 having astacked-layer structure was formed to a thickness of 40 nm as follows:2mFBPDBq, PCBBiF, and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]) were deposited by co-evaporation to athickness of 20 nm so that the mass ratio of 2mFBPDBq to PCBBiF and[Ir(dppm)₂(acac)] was 0.7:0.3:0.05, and then 2mFBPDBq, PCBBiF, and[Ir(dppm)₂(acac)] were deposited by co-evaporation to a thickness of 20nm so that the mass ratio of 2mFBPDBq to PCBBiF and [Ir(dppm)₂(acac)]was 0.8:0.2:0.05.

Next, the electron-transport layer 814 was formed over thelight-emitting layer 813.

First, 2mFBPDBq was deposited by evaporation to a thickness of 20 nm andthen bathophenanthroline (abbreviation: Bphen) was deposited byevaporation to a thickness of 10 nm, whereby the electron-transportlayer 814 was formed.

Next, lithium fluoride was deposited by evaporation to a thickness of 1nm over the electron-transport layer 814, whereby the electron-injectionlayer 815 was formed.

Finally, aluminum was deposited to a thickness of 200 nm over theelectron-injection layer 815, whereby a second electrode 803 functioningas a cathode was formed. Through the above-described steps, thelight-emitting elements 1 and 2 were fabricated. Note that in all theabove evaporation steps, evaporation was performed by aresistance-heating method.

Table 1 shows element structures of the light-emitting elements 1 and 2fabricated as described above.

TABLE 1 Light-emitting element 1 Light-emitting element 2 Firstelectrode ITSO (110 nm) ITSO (110 nm) Hole-injection DBT3P-II:MoOxDBT3P-II:MoOx layer (4:2, 20 nm) (4:2, 20 nm) Hole-transport BPAFLPBPAFLP layer (20 nm) (20 nm) Light-emitting 2mFBPDBq:PCBBiF:2mFBPDBq:PCBBiF: layer [Ir(tBuppm)₂(acac)] [Ir(dppm)₂(acac)](0.7:0.3:0.05, 20 nm) (0.7:0.3:0.05, 20 nm) 2mFBPDBq:PCBBiF:2mFBPDBq:PCBBiF: [Ir(tBuppm)₂(acac)] [Ir(dppm)₂(acac)] (0.8:0.2:0.05, 20nm) (0.8:0.2:0.05, 20 nm) Electron-transport 2mFBPDBq (20 nm) 2mFBPDBq(20 nm) layer Bphen (10 nm) Bphen (10 nm) Electron-injection LiF LiFlayer (1 nm) (1 nm) Second electrode Al (200 nm) Al (200 nm)

The fabricated light-emitting elements 1 and 2 were each sealed in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air (specifically, a sealant was applied onto outer edges of theelements, and UV treatment was performed first and then heat treatmentwas performed at 80° C. for 1 hour).

<<Operation Characteristics of Light-Emitting Elements 1 and 2>>

Operation characteristics of the fabricated light-emitting elements 1and 2 were measured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 9 shows current voltage-luminance characteristics of thelight-emitting elements 1 and 2. In FIG. 9, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V). FIG.10 shows luminance-current efficiency characteristics of thelight-emitting elements 1 and 2. In FIG. 10, the vertical axisrepresents current efficiency (cd/A) and the horizontal axis representsluminance (cd/m²).

Table 2 shows initial values of main characteristics of thelight-emitting elements 1 and 2 at a luminance of approximately 1000cd/m². Note that green light emission originating from[Ir(tBuppm)₂(acac)], which was used as a guest material of thelight-emitting layer, was obtained from the light-emitting element 1 andorange light emission originating from [Ir(dppm)₂(acac)], which was usedas a guest material of the light-emitting layer, was obtained from thelight-emitting element 2.

TABLE 2 Light-emitting element 1 Light-emitting element 2 Voltage (V)2.9 3 Current (mA) 0.036 0.05 Current density 0.89 1.3 (mA/cm²)Chromaticity (0.41, 0.58) (0.55, 0.45) coordinates (x, y) Luminance(cd/m²) 910 1100 Current efficiency 100 86 (cd/A) Power efficiency 11090 (lm/W) External quantum 27 32 efficiency (%)

Next, the light-emitting element 1 was subjected to a reliability test.A comparison light-emitting element 3 was additionally fabricated andcompared with the light-emitting element 1. Note that for thelight-emitting layer 813 and the electron-transport layer 814 in thecomparison light-emitting element 3,2mDBTBPDBq-II, which does not have afluorene skeleton, was used instead of the heterocyclic compound(2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mFBPDBq)) which is one embodiment of the presentinvention and used for the light-emitting layer 813 and theelectron-transport layer 814 in the light-emitting element 1. Thestructural formula of 2mDBTBPDBq-II is shown below.

A method of fabricating the comparison light-emitting element 3 is thesame as the above-described method. Table 3 shows the element structureof the comparison light-emitting element 3.

TABLE 3 Comparison light-emitting element 3 First electrode ITSO (110nm) Hole-injection DBT3P-II:MoOx layer (4:2, 20 nm) Hole-transportBPAFLP (20 nm) layer Light-emitting 2mDBTBPDBq-II:PCBBiF: layer[Ir(tBuppm)₂(acac)] (0.7:0.3:0.05 (20 nm) 2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.05 (20 nm)) Electron-transport2mDBTBPDBq-II (20 nm) layer Bphen (10 nm) Electron-injection LiF layer(1 nm) Second electrode Al (200 nm)

Results of the reliability test are shown in FIG. 11. In FIG. 11, thevertical axis represents normalized luminance (%) with an initialluminance of 100% and the horizontal axis represents driving time (h) ofthe light-emitting elements. Note that in the reliability test, thelight-emitting element 1 and the comparison light-emitting element 3were driven under the conditions where the initial luminance was set to5000 cd/m² and the current density was constant.

While the light-emitting element 1 includes the heterocyclic compound(2mFBPDBq) which is one embodiment of the present invention in thelight-emitting layer, the comparison light-emitting element 3 includes2mDBTBPDBq-II in the light-emitting layer. The light-emitting element 1formed using the heterocyclic compound (2mFBPDBq) which is oneembodiment of the present invention was found to have higher reliabilityand a longer lifetime than the comparison light-emitting element 3formed using a heterocyclic compound that does not have such astructure, because the heterocyclic compound used to form thelight-emitting element 1 has a structure in which adibenzo[f,h]quinoxaline ring is bonded to a fluorene skeleton through anarylene group.

Example 3

This example shows examination results of the solubility of theheterocyclic compound which is one embodiment of the present invention.

The heterocyclic compound which is one embodiment of the presentinvention and used in this example was 2mFBPDBq (sample 1). Note that2mFBPDBq was synthesized by the synthesis method described in Example 1.In addition, the compound used for comparison was 2mDBTBPDBq-II(comparison sample 2). The purity of each compound was 99.9%. Thestructural formulae of the compounds are shown below.

The solvents used in this example were the four kinds of solvents:toluene, chloroform, ethyl acetate, and acetone.

A method of examining the solubility of the compound of each sample isdescribed. First, 10 mg of the compound was put into a small bottle andto this was added 1 mL of a solvent. Then, whether the compound wasdissolved at room temperature or not was checked. When the compound wasnot dissolved at room temperature, ultrasonic wave irradiation and thenheating using a dryer were performed, so that whether the compound wasdissolved was checked.

When the compound was not dissolved after heating, the volume of thesolvent was increased to 10 mL, so that whether the compound wasdissolved at room temperature was checked. When the compound was notdissolved at room temperature, ultrasonic wave irradiation and thenheating using a dryer were performed, so that whether the compound wasdissolved was checked.

The examination results of the solubility are shown in Table 4.

TABLE 4 Chloro- Ethyl Toluene form acetate Acetone Sample 1 2mFBPDBq ◯ ◯□ □ Comparison 2mDBTBPDBq-II X X X X sample 2 (Legends) ⊚ dissolved at10 mg/mL at room temperature U ◯ dissolved at 10 mg/mL when heated dissolved at 10 mg/mL when heated, but precipitated when returned toroom temperature Δ dissolved at 10 mg/10 mL at room temperature □dissolved at 10 mg/10 mL when heated ▪ dissolved at 10 mg/10 mL whenheated, but precipitated when returned to room temperature X notdissolved (leaving an undissolved residue)

The results in this example reveal that the heterocyclic compound(sample 1:2mFBPDBq) which is one embodiment of the present invention hashigher solubility than the comparison compound (comparison sample2:2mDBTBPDBq-II). High solubility facilitates separation or purification(e.g., extraction, column chromatography, and recrystallization), whichis performed by dissolving the compound in an organic solvent, so thatimpurities can be easily removed. In the case of the heterocycliccompound which is one embodiment of the present invention, purificationby sublimation is performed after a considerable reduction in the amountof impurities remaining after separation or purification by dissolvingthe compound in an organic solvent; thus, the compound can easily behighly purified because of the high solubility in organic solvents.Furthermore, the number of steps of the purification by sublimation canbe reduced. Thus, by using such a high-purity heterocyclic compound fora light-emitting element, initial deterioration is suppressed and thelight-emitting element is made more reliable.

This application is based on Japanese Patent Application serial no.2014-091395 filed with the Japan Patent Office on Apr. 25, 2014, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A compound represented by a formula (G0),A-Ar—B  (G0) wherein A represents a dibenzo[f,h]quinoxalinyl group, Brepresents a substituted or unsubstituted fluorenyl group, and Arrepresents a substituted or unsubstituted arylene group having 6 to 25carbon atoms.
 2. The compound according to claim 1, wherein B is asubstituted or unsubstituted 2-fluorenyl group.
 3. The compoundaccording to claim 1, wherein B is represented by a formula (α):

and wherein each of R¹¹ to R¹⁹ independently represents hydrogen, analkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12carbon atoms.
 4. The compound according to claim 1, wherein B isrepresented by a formula (β):

and wherein each of R¹⁷ and R¹⁸ independently represents hydrogen, analkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12carbon atoms.
 5. The compound according to claim 1, wherein the compoundis represented by a formula (G1):

wherein one of R¹ to R¹⁰ is represented by a formula (G1-1) and theothers of R¹ to R¹⁰ independently represent hydrogen or an alkyl grouphaving 1 to 6 carbon atoms, and wherein B represents a substituted orunsubstituted fluorenyl group, and Ar represents a substituted orunsubstituted arylene group having 6 to 25 carbon atoms.
 6. The compoundaccording to claim 5, wherein B is a substituted or unsubstituted2-fluorenyl group.
 7. The compound according to claim 5, wherein B isrepresented by a formula (α):

and wherein each of R¹¹ to R¹⁹ independently represents hydrogen, analkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12carbon atoms.
 8. The compound according to claim 5, wherein B isrepresented by a formula (β):

and wherein each of R¹⁷ and R¹⁸ independently represents hydrogen, analkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12carbon atoms.
 9. A light-emitting element comprising the compoundaccording to claim
 1. 10. A light-emitting element comprising: an ELlayer between a pair of electrodes, wherein the EL layer comprises thecompound according to claim
 1. 11. A light-emitting element comprising:an EL layer between a pair of electrodes, wherein the EL layer comprisesa light-emitting layer, and wherein the light-emitting layer comprisesthe compound according to claim
 1. 12. A light-emitting elementcomprising: an EL layer between a pair of electrodes, wherein the ELlayer comprises a light-emitting layer, wherein the light-emitting layercomprises three or more kinds of organic compounds, and wherein one ofthe three or more kinds of organic compounds is the compound accordingto claim
 1. 13. A light-emitting device comprising: the light-emittingelement according to claim 9; and a transistor or a substrate.
 14. Anelectronic appliance comprising: the light-emitting device according toclaim 13; and a microphone, a camera, a button for operation, anexternal connection portion, or a speaker.
 15. A lighting devicecomprising: the light-emitting device according to claim 13; and ahousing, a cover, or a support.
 16. A compound represented by a formula(100)


17. A light-emitting element comprising the compound according to claim16.
 18. A light-emitting element comprising: an EL layer between a pairof electrodes, wherein the EL layer comprises the compound according toclaim
 16. 19. A light-emitting element comprising: an EL layer between apair of electrodes, wherein the EL layer comprises a light-emittinglayer, and wherein the light-emitting layer comprises the compoundaccording to claim
 16. 20. A light-emitting element comprising: an ELlayer between a pair of electrodes, wherein the EL layer comprises alight-emitting layer, wherein the light-emitting layer comprises threeor more kinds of organic compounds, and wherein one of the three or morekinds of organic compounds is the compound according to claim
 16. 21. Alight-emitting device comprising: the light-emitting element accordingto claim 17; and a transistor or a substrate.
 22. An electronicappliance comprising: the light-emitting device according to claim 21;and a microphone, a camera, a button for operation, an externalconnection portion, or a speaker.
 23. A lighting device comprising: thelight-emitting device according to claim 21; and a housing, a cover, ora support.